“Family molding” is a term used to refer to the molding of different parts in a given mold set. In the case of stack molds, different parts may be produced on different levels. Sometimes, although not exclusively so, the parts may form components of a larger assembly, such as a container and its lid.
A common arrangement for delivering melt to a mold is referred to as a “hot runner system”. Two variants of hot runner systems are “valve gate” hot runners and “hot tip” hot runners. Either uses a nozzle to introduce melt into a gate which provides an inlet to a space defined between core and cavity parts of a mold. A valve gate system has a retractable valve pin extending axially along the nozzle into the gate for opening and closing the gate.
A hot tip system controls the temperature of a nozzle tip which registers with the gate to control melt flow. Heat is removed to solidify melt in the tip thereby blocking the tip. Heat is added to remelt the solidified melt and recommence melt flow through the nozzle.
Valve gated systems have a lower shear rate at the gate providing more gentle flow. Valve gated systems are however more expensive and wear prone than hot tip systems.
One application for hot runner systems is in what is aptly named as “in mold labelling” or “IML”. In IML, one or more labels is/are placed into a mold cavity prior to mold closing. The mold is subsequently closed and melt injected to cause the label to fuse into the melt and appear on the outer face(s) of a finished part.
In some applications, one face or side (typically the bottom face or side) may not require a label. For a rectangular container this may be referred to as “four-sided labelling”. In other applications labels will be required on all sides or faces which, in the case of a rectangular container may be referred to as “five-sided labelling”. The terms “four-sided” and “five-sided” are used herein for convenience bearing in mind that the challenges posed by either also translate into other container configurations. For example a conical or cylindrical container may have one wraparound label (analogous to four sides) and may or may not have a label requited on its bottom or base (analogous to the “fifth” side). Also, containers with other shapes may be contemplated. Furthermore labels may be desired on the “bottom” face or side but not on all of the adjoining sides (such as in “three-sided” labelling).
In general, hot tip arrangements don't work well in IML situations where a label is present opposite to the nozzle, such as in a three or five-sided label for a rectangular container having a label and a melt entry point on its base. Generally in such situations the melt would damage the label and get past the edges of the label to mask its face. Hot tip arrangements however work well for three or four-sided labelling of a similar container with no label on its base.
According to traditional mold design, molds and runner systems were designed as a dedicated set and changing from one part configuration to another required in effect replacing virtually everything between the fixed and movable platens of the injection molding machine. Furthermore, changing parts also required changing any mold take-off arrangements (such as robotics) as a new set would be unlikely to discharge parts in a location similar to the previous set.
In order to make parts economically with dedicated mold and runner arrangements, a rather significant production run would be required. Dedicated systems are expensive to build and significant downtime is required to effect changeover. The associated costs for using dedicated arrangements will make molding in some markets uneconomical because the volume won't justify the cost.
Consider for example a rectangular container and lid as a family mold. The same container may be desired by different customers for different products. The different customers will have different labelling requirements, not only graphically but also as to whether or not all of the faces of the containers are to be labelled. Accordingly, situations may arise where the same general container shape may require valve gated runners or hot tip runners depending on labelling requirements. Furthermore a common lid may be usable with different containers. In order to serve such markets with minimal capital investment, versatile mold arrangements are required.
It is an object of the present invention to provide a molding arrangement wherein different mold sets may be readily interchanged without changing runner systems and wherein at least portions of a runner system may be readily interchanged between hot tip and valve gate designs in order to effect corresponding mold changes such as may be required for different labelling requirements.